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Three stoichiometric dolomite rocks have been shortened
in triaxial compression experiments at T = 500 - 800 C, Pc =
300 - 400 MPa, and e =
10&endash;7 - 10&endash;5 s-1. Natural dolomite starting
materials include 1) Blair dolomite (Ca 1.027 Mg 0.973
(CO3)2) investigated earlier (Handin et al., 1967; Hugman
and Friedman, 1979) with a grain size of <10 µm, 2)
Kern Mountains dolomite (Ca 1.008 Mg 0.992(CO3)2), from
eastern Nevada, with a grain size of 80 µm, and 3)
Madoc dolomite (Ca 1.000 Mg 1.000 (CO3)2, from Ontario,
Canada, with a grain size of 240 µm. Blair dolomite
contains as much as 10% secondary phases, including quartz
and feldspar, while Kern and Madoc dolomites are
monomineralic, with only traces of impurity minerals.
Microprobe analyses indicate that Fe is below detection
limits for all three dolomites.
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Over all conditions investigated, Blair dolomite is
strong, with differential stresses reaching 800 MPa and
brittle faulting following soon after yielding, while the
coarser Kern and Madoc dolomites exhibit lower strengths
(200 - 600 MPa) and finite strains reach 15% without
macroscopic failure. Microstructures indicate that strains
are accommodated by mechanical twinning on f-planes (mostly
at the higher differential stresses) and intracrystalline
slip. For a given set of conditions, flow strengths of Kern
and Madoc dolomites are comparable and they vary
systematically with temperature and strain rate, with
similar sensitivities to T and e
observed by Barber et al. (1994) for Crevola dolomite (grain
size ~ 1 mm).
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